用STEREO和HINODE观测到的两类动态冷日冕结构
Two Types of Dynamic Cool Coronal Structures Observed with STEREO and HINODE
摘要：
太阳日冕环在其形成和喷发阶段表现出显着的等离子体运动。另一方面，动态冷日冕结构经常被观察到沿着日冕环传播。在本文中，我们报告了两种类型的动态冷日冕结构的发现，并描述了它们的基本性质。利用日地关系天文台（STEREO）的极紫外成像仪（EUVI）304埃的EUV图像和HINODE上的太阳光学望远镜（SOT）的Ca II滤波图，我们研究了极紫外弧的演化和冷日冕结构的运动学。EUV 304埃的观测表明，一个导弹状的等离子体团沿着拱形轨道移动，平均速度为31 km/s。约3小时后，沿轨迹形成等离子体弧，弧顶逐渐消失，同时弧腿等离子体向下流向弧脚。在星拱形成和消失的过程中，SOT Ca II图像探测了星拱下的动态冷冠结构。通过跟踪这些结构，我们将它们分为两种类型。Ⅰ型为线状，向下流动，平均速度较大，为72 km/s，最后在色球层高度结合成环状纤丝。第二类是可变形的，有时滚动，因为它以37公里/秒的较小速度向下流动，然后在色球层中消失。这两种结构可能是由不同的磁位形控制的。
英文摘要：
Solar coronal loops show significant plasma motions during their formation and eruption stages. Dynamic cool coronal structures, on the other hand, are often observed to propagate along coronal loops. In this paper, we report on the discovery of two types of dynamic cool coronal structures, and characterize their fundamental properties. Using the EUV 304 angstrom images from the Extreme UltraViolet Imager (EUVI) telescope on the Solar TErrestrial RElation Observatory (STEREO) and the Ca II filtergrams from the Solar Optical Telescope (SOT) instrument on HINODE, we study the evolution of an EUV arch and the kinematics of cool coronal structures. The EUV 304 angstrom observations show that a missile-like plasmoid moves along an arch-shaped trajectory, with an average velocity of 31 km/s. About three hours later, a plasma arch forms along the trajectory, subsequently the top part of the arch fades away and disappears, meanwhile the plasma belonging to the two legs of the arch flows downward to the arch feet. During the arch formation and disappearance, SOT Ca II images explore dynamic cool coronal structures beneath the arch. By tracking these structures, we classify them into two types. Type I is threadlike in shape and flows downward with a greater average velocity of 72 km/s, finally it combines a loop fibril at chromospheric altitude. Type II is shape-transformable and sometimes rolling as it flows downward with a smaller velocity of 37 km/s, then disappears insularly in the chromosphere. It is suggested that the two types of structures are possibly controlled by different magnetic configurations.
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